In an image forming apparatus with an electrophotographic system, a charging unit electrically charges a photosensitive drum in advance, and an exposure unit emits light on a surface of the photosensitive drum. Then, an electrostatic latent image is formed on the surface of the photosensitive drum. A developing unit bears toner. The toner adheres to the electrostatic latent image to form a toner image. The toner image is transferred on and fixed to a sheet.
After the toner is transferred on the sheet, a small quantity of the toner may not be transferred and remain on the surface of the photosensitive drum. The remaining toner may affect the formation of the next image(s). Therefore, a device that cleans the surface of the photosensitive drum has been utilized.
More specifically, a cleaning roller and a cleaning blade may be used to contact the surface of the photosensitive drum. The toner contains a very small quantity of an external additive. The cleaning roller uses the toner containing the external additive to remove substances, such as corona discharge products adhering to the surface of the photosensitive drum.
Also, a scraper contacts the cleaning roller. The scraper controls the thickness of a layer of the toner being held on the cleaning roller. If the thickness of the layer of the toner is uneven, a smaller-thickness portion of the layer of the toner may not effectively polish the surface of the photosensitive drum. In contrast, in a larger-thickness portion of the layer of the toner, the electric charge of the toner is hardly discharged, and the photosensitive drum may be electrostatically damaged. Unfortunately, the above mentioned conventional structure still has a problem in providing for a proper quantity of the remaining toner adhering to and being held by the cleaning roller.
This is because the scraper only line contacts the cleaning roller in a counter direction with respect to a rotation direction of the cleaning roller. In other words, the scraper contacts the cleaning roller only by point contact in a sectional view along a plane substantially orthogonal to a rotation axis of the cleaning roller. Hence, most of the remaining toner is scraped away from the cleaning roller and is hardly held by the cleaning roller.
In this state, it is difficult to continuously and effectively polish the surface of the photosensitive drum. Also, the external additive in the toner may adhere to the surface of the photosensitive drum, be separated from the surface of the photosensitive drum, and contaminate the charging unit.